Reliability Calculator

For components with a constant failure rate (the flat portion of the bathtub curve, during normal operating life), the reliability function is R(t) = e^(-lambda * t), where lambda is the failure rate (failures per hour) and t is the mission time in hours. This assumes failures are random and independent, with no wear-out (valid for electronics during normal operating life).

MTBF (Mean Time Between Failures) is the average time between consecutive failures for a repairable system. MTBF = 1 / failure_rate. For a component with a failure rate of 0.0001 failures/hour (1 failure per 10,000 hours), MTBF = 10,000 hours. MTTF (Mean Time To Failure) is used for non-repairable items and has the same formula.

The bathtub curve shows how component failure rate changes over its lifetime. Early life (infant mortality): high failure rate as defects manifest. Normal operating life: constant low failure rate (random failures). Wear-out: increasing failure rate as components age and degrade. The exponential reliability function applies to the constant failure rate period. Weibull distributions model all three phases.

FIT (Failures In Time) is a unit equal to 1 failure per 10^9 device-hours. To convert to failures/hour: lambda = FIT / 10^9. A component rated at 100 FIT has a failure rate of 0.0000001 failures/hour and an MTBF of 10,000,000 hours. FIT ratings are commonly used for electronic components in datasheets.

Reliability targets depend on the mission profile and consequences of failure. Safety-critical aerospace systems target R(t) above 0.999999 for their mission duration. Medical devices: R(t) above 0.9999. Commercial IT systems: R(t) above 0.99 for a typical service interval. Set targets based on the business impact of failure, regulatory requirements, and warranty cost models.